347
FXUS63 KDTX 121756
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
156 PM EDT Sat Jul 12 2025

.KEY MESSAGES...

- Seasonable temperatures in the mid 80s tomorrow, then warming back
to around 90 degrees on Tuesday.

- Dry start to the week, but showers and thunderstorms likely return
Wednesday-Thursday.

&&

.AVIATION...

Several gravity waves emanated away from the trough over the Midwest
this morning initiated convection a few hours earlier than
anticipated today. With the lead line exiting the area at press
time, we look toward the next few hours for any additional
convection. The next line has initiated over MBS and will now work
eastward but confidence in how this line will act over the next few
hours is low. Will hedge the tempo forward in time a few hours
thinking that this next line may be the final chance this evening as
drier air is spreading across SW Lower toward the area which will
further lower chances. So, tempo TSRA through about 20-21Z with only
isolated activity after that. The cold front will work through
tonight possibly touching off a few showers, otherwise expecting a
sct low VFR/MVFR deck tonight before skies improve Sunday. Gusty
winds this afternoon will decrease and turn westerly tonight with
the frontal passage.

For DTW/D21 Convection...There remains a chance of thunderstorms
this afternoon mainly before 21Z. Only isolated activity is expected
this evening with mainly dry conditions tonight. Gusty winds will be
the primary threat with any storm.

THRESHOLD PROBABILITIES...

* Low for ceiling 5000 ft or less outside of thunderstorms today and
  this evening. Moderate with the cold front late tonight.

* Low for thunderstorms this afternoon.

&&

.PREV DISCUSSION...
Issued at 945 AM EDT Sat Jul 12 2025

UPDATE...

Low pressure and mid level jet max tracking through the Straights
this morning with a weak surface troughing extending south into
south central Lower Michigan. 12z DTX sounding showed good speed bump
around 800 MB, along with the pronounced surface based inversion,
which will need to be eroded. 700 MB temp also fairly warm at 9 C.
None-the-less, surface dew pts in the lower 70s with temps warming
toward 90 degrees around noon/by early afternoon will be sufficient
for SBcapes aoa 2500 J/kg. The issue is the upper level trough over
Minnesota and associated height falls/mid level cooling is not
looking to be a factor for us, and we will have to utilize a more
subtle height fall center/PV advection coming up from the western
Ohio Valley to support shower and thunderstorm development with the
weak low level trough/convergence sliding east through the day. Based
on timing and slightly backed flow due to marine influences, areas
over eastern areas of the CWA look to have greatest coverage of
storms and potential of severe storms. Precip loaded downbursts
producing wind gusts of 50-60 MPH being the main hazard, along with
torrential rainfall potentially producing localized flooding with
relatively slow movement of storms and possible training as outflow
boundaries get going. Update was mainly to adjust highest pops (70+)
over far eastern areas, and highlight noon-8 PM as the main window.

PREV DISCUSSION...
Issued at 356 AM EDT Sat Jul 12 2025

DISCUSSION...

Periodic convection with renewed potential for some severe
thunderstorms returns today as an active pattern holds firm over the
Great Lakes. Upstream convection exits into northern Lower through
the remaining morning hours while mid-level is underway over
Southeast Michigan. Thermodynamic profiles are still supportive of
an elevated mixed layer with over 500 J/kg of MUCAPE before deep-
layer southwest flow slides into the region. A shortwave trough with
a 50+ knot jet core at 500 mb ejects across western Lower today and
starts to phase with a more amplified trough tilting from neutral to
negative over the Upper Midwest.

Main corridor of CVA should largely reside west of the forecast area
as midday convection starts to initiate, likely between 16Z and 18Z.
This activity predominantly develops along the CAPE gradient, in the
vicinity of the western CWA border. Main plume of instability,
marked by MLCAPE of 1000-1500 J/kg, will quickly blossom and
overspread Southeast Michigan through the early afternoon hours.
Surface reflection from the parent wave takes a more north-
northeasterly track which slows the advance of its attendant cold
front. Wind progs indicate the more pronounced south-to-west wind
shift closer to 06Z (Sunday), thus the pre-frontal surface trough
axis will serve as the more important dynamic mechanism to amplify
convection. Perhaps more importantly, the majority of the latest NWP
suite supports surface-based free-convection with ELs above 35 kft
once surface dewpoints revisit the lower 70s and 2m temperatures
jump to near 90F within the expanding warm sector. Shear parameters
are not overwhelmingly impressive, but remain sufficient to help
organize some linear structures. Severe threat still mainly focused
on wind hazards (isolated gusts to 60 mph) and torrential rainfall.
For what it`s worth, ML data has carried higher severe wind
probabilities with run-to-run consistency. Also of note, prior to
the onset of precipitation, the greater Metro Detroit area could see
heat indices approach 100F, but it will be marginal since mid-70F
dewpoints appear to be the exception rather than the norm.

The front makes gradual inroads into Ontario late tonight which
corresponds to a drying locally, from west to east. Subset of CAMs
indicate a secondary storm response along the actually cold frontal
slope, but intensity should be significantly lower if this
materializes.

Post-frontal airmass characterized as cooler and drier for Sunday,
although temperatures should run near climatological averages (mid
80s). Can`t completely rule out a few showers for the extreme
southeast portion of the CWA with the slowed boundary. Longer
wavelength trough axis aloft then backs the temporarily zonal flow
aloft with little sensible fanfare. A rebound in geopotential
heights is in store for next week as synoptic-scale anticyclonic
gyre organizes over The Southeast. This promotes moderating thermal
profiles with negligible storm potential Monday and Tuesday. Zonal
jet centered over the 50th parallel delivers a weak wave extending
into southern Lower Michigan as soon as Wednesday that could spur
convective activity. Model divergence has emerged in the medium-
range solutions for the extent of thermal troughing over the state,
but NBM output exudes confidence with a cold FROPA by Friday.

MARINE...

Renewed chances for showers and thunderstorms today ahead of and
along a cold front, which brings chances for strong to severe
thunderstorm development capable of producing wind gusts aoa 35
knots. Winds veer toward the southwest then continue toward the west
after the passage of the front. Mainly dry conditions and light
winds expected in the wake of the front, and through early next
week.

HYDROLOGY...

Some heavy showers and storms are likely today as a hot and humid
airmass builds back into the region. The environment will support
pockets of heavy downpours with rainfall rates possibly exceeding 2
inches per hour. Localized flooding concerns exist for some areas
that experience clustering of cells. Flooding threat will largely be
for small streams, low-lying roadways, and otherwise poorly drained
areas. Activity should wane from west to east early tonight as drier
weather settles in for the rest of the weekend and early next week.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422.

Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

$$

AVIATION.....DRK
UPDATE.......SF
DISCUSSION...KGK
MARINE.......AM/KGK
HYDROLOGY....KGK


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